Most known electronic dosimeters, in particular portable dosimeters, are limited in the low energy range for reasons related to measuring the dose absorbed by an appropriate material, which will be very dependent on this material under about 50 keV.
In fact, dosimetry consists in measuring, from a measure obtained in general by means of a silicon based detector, the dose theoretically absorbed by human tissues.
At high energy, i.e. at energy exceeding about 100 keV, the dose left in the human tissues and the response of such a detector are simply linked together by a proportionality factor which is hardly energy dependent.
Consequently, compensation is easy.
On the other hand, as soon as energy is less than 100 keV, this factor begins to be energy dependent.
This makes it necessary to fine-tune the dosimeter's configuration allowing, among others, for the addition of absorbent materials in front of the detector itself.
However, the mitigation in such absorbent materials is all the more important since the energy of incident X and gamma radiation is low.
Consequently, the dosimeter is essentially no longer responsive to radiation with energy values of less than 50 keV.
And yet, in the field of radiation protection, a low energy radiation involves a risk, especially for the first millimeter of skin where a very large superficial dose can be left.
Therefore, in the field of radiation protection, there is a strong demand for the development of dosimeters with a low energy limit on the order of 10 keV, or even less.
Of course, this demand has increased due to the emergence of new European standards as far as radiation protection is concerned.
In particular, in the case of portable dosimeters, where the X and gamma radiation detector used is a standard silicon based photodiode, there is no simple technical solution available regarding the above-mentioned limitation.
As mentioned above, the 50 keV energy limitation is substantially due to the fact that filters have to be used for compensating the detector's response in terms of dose measuring.
Unfortunately, these filters function as very efficient absorbents at low energy, so that most known dosimeters are not responsive to low energy radiation.